FLUORESCENT COATING FOR ROAD MARKINGS

Abstract: A fluorescent coating which fluoresces when illuminated with light within the ultraviolet wavelength range, wherein the coating is intended primarily for different kinds of road markings and includes material containing pigment which emits a colour when irradiated with light within the visible wavelength range and material which fluoresces when illuminated with light within the ultraviolet wavelength range. The invention is characterized in that the material that fluoresces when illuminated with light within the ultraviolet wavelength range has been chosen so that it fluoresces essentially in a wavelength range of 455-555 nanometers.

Description: FLUORESCENT COATING FOR ROAD MARKINGS The present invention relates to a fluorescent coating which fluoresces in the presence of light within the ultraviolet wavelength range. The invention relates particularly to a coating intended for road markings, for instance markings on road verges, centre line markings, stop lines, right-of-way markings, lane arrows, pedestrian crossings, and like markings. The coating can also be applied to different types of signs for instance. The fact that the full beam of a car brightly illuminates the surroundings in front of the car is a generally known problem. The full beam of a vehicle will also dazzle oncoming motorists, however. When the vehicle is driven on dipped headlights, so as not to dazzle oncoming motorists, the surroundings in front of the vehicle are not illu inat- ed satisfactorily. Normally, however, the amount of light provided by dipped headlamps is sufficient for the driver to see the road ahead well enough to drive the vehicle. However, the ability to discern objects on the road, such as road markings and other stationary markings, as well as people, is much poorer on dipped headlamps than on full beam. One desire, which is becoming more and more pronounced, is that vehicles shall be equipped with lamps that emit ultraviolet light. Such light causes a number of different paints or pigments to fluoresce to a greater or lesser extent. It has become more general in recent times to use so-called daylight pigments or paints, i.e. paints which when illuminated by ultraviolet (UV) light emit light of visible wavelength. Light clothing also fluoresces rela¬ tively well when illuminated with ultraviolet light. If vehicles were able to transmit ultraviolet light, it would be possible to paint road verge-posts, road signs, etc., either totally or partially with so-called daylight paints to a larger extent than is now the case, with the intention of enhancing traffic safety. It is previously known to produce road markings which fluoresce when illuminated with ultraviolet light. One such coating is known from U.S. 3,253,146. This coating is produced by mixing a pigment, which fluoresces when illuminated with ultraviolet light, with a transparent carrier or matrix. The known technique used generally for utilizing ultravio- let fluorescent paints, so-called daylight paints, resides in the use of a pigment which fluoresces when illuminated by ultraviolet light. Swedish Patent Specification 9002413-4 describes, on the other hand, a road marking which is characterized in that the material that fluoresces when illuminated with light within the ultraviolet wavelength range is comprised of glass balls or glass pieces produced from a glass composi¬ tion that has been doped with a dope substance which causes the glass in the glass balls or glass pieces to fluoresce when illuminated with ultraviolet light. Tests carried out on ultraviolet fluorescing road signs have shown surprisingly that the measurements taken of the intensity of the visible light emitted from the markings do not agree with how people experience the strength of the light emitted by said markings. This means that the best fluorescent substance cannot be chosen with the aid of measuring instruments, as earlier supposed. The present invention provides a marking which can be seen better than earlier known markings. The present invention thus relates to a fluorescent coating which fluoresces when illuminated with light within the ultraviolet wavelength range, said coating being intended primarily for different types of road markings and includes a material that contains a pigment for emitting one colour when illuminated with light within the visible wavelength range and material which fluoresces when illuminated with light within the ultraviolet wavelength range, and is characterized in that the material which fluoresces when illuminated with light within the ultraviolet wavelength range has been chosen to fluoresce essentially in a wavelength range of 455-555 nanometers. The invention will now be described in more detail. It is known that the sensitivity of the human eye varies with the wavelength of light. The sensitivity of the eye also varies with different levels of illumination and whether foveal sight or peripheral sight is meant. By foveal sight is meant that the gaze is concentrated straight forwards, where the focus of the eye is sharpest. The foveal point covers only about 0.5 degrees. The sensitivity of the eye has earlier been documented and is disclosed in standard works, for instance IES Lighting Handbook, 1984, Reference Volume. This work deals with an investigation into the sensitivity of the eye in the case of foveal sight under normal lighting levels, and sight that lies outside the foveal point at normal lighting levels. Scoptic sight, i.e. the ability to see in the dark, has also been investigated and compared with photopic sight, i.e. the ability to see in normal daylight. It has been established that the eye takes about 60 minutes to adapt fully to darkness. It has been found that none of the aforesaid cases apply when driving in the dark. This is because the eye does not become fully adapted to the dark, since this takes 60 minutes to achieve, and since the eye looks at an illumi- nated part of the road. It has been found that the eye is situated in an intermediate phase, so-called mesopic sight. The lighting levels vary between scoptic and photopic levels. Both foveal and peripheral sight are also used. Added to this is the dazzling effect of the occasional oncoming vehicle. The perception of the eye, i.e. its ability to discern an object, varies greatly with for instance the state of tiredness, the mental state, the expectation of seeing an object ahead, the stress to which the driver is subjected mentally by the surroundings, and colour content. The anticipation of seeing an object is of particular interest with regard to driving a vehicle. A number of tests were carried out to establish the difference between discerning a static object and discern¬ ing a dynamic traffic object. It was found that in order to discern an object in dynamic traffic, the contrast differ¬ ence required was 10-30 times higher than the contrast difference required to discern a static object. However, expectation with regard to road markings in the form of verge lines and, to some extent, verge posts is extremely high, and consequently the eye is well able to discern a verge demarcation line in relatively low contrast conditions, even in dynamic traffic. It has also been established that the eye is able to discern road markings at relatively low luminesce levels. It has also been established that the ability to discern fluorescent objects at low levels of illumination differs from the ability to discern non-fluorescent objects. The invention is based on the realization that when an edge line is produced in a fluorescent material whose fluorescence is adapted to peripheral sight and mesopic sight, the adaptation to mesopic sight will cause the gaze of the viewer to be moved further along the road, at the same time as the adaptation to peripheral sight will cause the edge line to be discerned clearly by the peripheral sight, even from close distances. The fact that the gaze of the viewer is moved further along the road in combination with a high degree of expectation, causes a fluorescent edge line to be discerned clearly from much further distances than when using conventional edge lines conventional headlamps. According to the present invention, the material that fluoresces when illuminated with light within the ultravio¬ let wavelength range is chosen to fluoresce essentially in a wavelength range of 455 and 555 nanometers. This provides the aforesaid effect. It can be mentioned by way of example that when carrying out practical tests with a vehicle equipped with headlamps that emitted conventional visible light and ultraviolet light, the following results were obtained with regard to the distances from which the driver was able to clearly discern verge markings. Illumination Verge Marking Normal dipped lights Conventional Normal dipped lights Fluorescent Normal dipped lights + ultraviolet light Fluorescent Normal dipped lights Conventional Normal dipped lights Fluorescent Wet 78 Normal dipped lights + ultraviolet light Fluorescent Wet 125 It will be obvious from this Table that visibility is very greatly improved when applying the present invention. According to one preferred embodiment, the fluorescent material will fluoresce in a substantially narrower wavelength range than that given above, namely between 470 and 540 nanometers. According to a further preferred embodiment, the fluores- cent material is chosen so that its colour impression relating to the colour of the fluorescence within said wavelength range will lie between a blue-violet colour and a greenish colour. When the verge lines or other markings are white, it is preferred that the fluorescent material chosen is one which emits the major part of its fluorescence at a wavelength of less than 500 nanometers. According to another preferred embodiment, the fluorescent material is chosen so that it will be activated to maximum fluorescence when irradiated with ultraviolet light within the wavelength range of 340-400 nanometers, preferably within the wavelength range of 350-380 nanometers. It is namely within this wavelength range that vehicle headlamps that emit ultraviolet light provide a maximum light effect. In order to obtain a good effect also in daylight and at dusk, it is advantageous for the fluorescent material also to be activated by incident ultraviolet radiation that has a wavelength of about 400 nanometers. There are a large number of commercially available sub¬ stances which fluoresce within different wavelength ranges and which are suitable for use when practicing the inven¬ tion. Many substances emit visible light within a given spectrum, although the major part of the visible light is found within a given wavelength range. The above remarks and the features set forth in the following Claims shall be read against this background. Typical fluorescent compounds or substances contain zinc sulphide (ZnS) with additives of silver (Ag) , sulphur (S) and cadmium (Cd) . A large number of other compounds are available, and the person skilled in this art may select the compound or compounds that is/are most suited to the purpose of the present invention and to existing specifica¬ tions. The present invention is not therefore considered to be restricted to any particular fluorescent compound or substance, but can be varied within the scope of the following Claims.

Claims: CLAIMS 1. A fluorescent coating which fluoresces when illuminated with light within the ultraviolet wavelength range, wherein the coating is intended primarily for different kinds of road markings and includes material containing pigment which emits a colour when irradiated with light within the visible wavelength range and material which fluoresces when illuminated with light within the ultraviolet wavelength range, characterized in that the material that fluoresces when illuminated with light within the ultraviolet wavelength range has been chosen so that it fluoresces essentially in a wavelength range of 455-555 nanometers. 2. A fluorescent coating according to Claim l, character¬ ized in that the fluorescent material fluoresces substantially in a wavelength range of between 470 and 540 nanometers. 3. A fluorescent coating according to Claim 1 or 2, characterized in that the fluorescent material is chosen so that its colour impression within said wavelength range lies between a blue-violet colour and a greenish colour. 4. A fluorescent coating according to Claim 1 or 2, characterized in that when verge lines or other markings are white, the fluorescent material is chosen so that the major part of its fluorescence is emitted at a wavelength below 500 nanometers. 5. A fluorescent coating according to Claim 1, 2, 3 or 4, characterized in that the fluorescent material is chosen so that it is activated to maximum fluorescence by incident ultraviolet radiation within the wavelength range of 340- 400 nanometers, preferably within the wavelength range of 350-380 nanometers. 6. A fluorescent coating according to Claim 5, character¬ ized in that the fluorescent material is also activated by incident ultraviolet radiation having a wavelength of about 400 nanometers.

Inventors: FAST PEDER, FAST, PEDER
Applicants: FAST PEDER, ULTRALUX AB, FAST, PEDER
Application year: 1994
Main classification: C09D5
IPC codes: C09D5, C09K11, E01F9